hesitation when revving engine!

Wikkd GT · 06-06-2003, 12:37 PM

I just noticed the other day and also today, that when I start up my 00 GT and the engine is cold, and I put it in neutral and give it some gas to rev it up, it's almost like it bogs down, like it wants to stall out. As if it's not getting enough fuel. Is this normal on the Mustang or is there something that needs to be changed? It only has 26,000 miles on it.

GTJules99 · 06-06-2003, 06:14 PM

My '99 does the same thing. I'm not sure if everyone is like that but it has done this since I bought it.

Badass_yellowGT · 06-08-2003, 10:28 PM

mines does not do that never has
anyways you should not rev a cold engine you can do damage let it idle to warm up. it could be caused by the o2 sensors being running in a cold start loop making the engine run to rich the sensors only work after complete engine warm up

mlambrecht82 · 06-09-2003, 04:30 AM

The sensors do work when the engine is cold, you have HO2S (heated oxygen sensors) so they heat up to over 600 degrees almost instantly, but the engine is in open loop, in other words it disregards the signal from the o2 sensors, until the engine coolant temp. has reached a certain level. When the engine is cold it dumps extra fuel in to help the car warm up faster. Once the engine is warm it monitors the o2 sensors to keep the car at stoichiometric. Check for Trouble codes using your instrument cluster and if nothing shows up then just wait for the car to warm up before you rev it. Especially if its been sitting for a while and all the oil has leaked down in to the pan, metal on metal is a bad thing, let the oil get inbetween them first.

XTheOwl · 06-09-2003, 11:40 AM

I get the same thing. ('00 GT) I'm not revin it cold, but when I go to back out of the driveway when its cool out, its very hesitent and threatens to stall.

xto

MajorTwit · 06-10-2003, 01:45 PM

Quote:

I get the same thing. ('00 GT) I'm not revin it cold, but when I go to back out of the driveway when its cool out, its very hesitent and threatens to stall.

My 00 GT does it often right after startup, seldom after a few seconds of idling. Gas quality seems to have a huge effect on this problem.

ajcolv · 06-12-2003, 10:24 AM

Quote:

Originally posted by mlambrecht82
The sensors do work when the engine is cold, you have HO2S (heated oxygen sensors) so they heat up to over 600 degrees almost instantly, but the engine is in open loop, in other words it disregards the signal from the o2 sensors, until the engine coolant temp. has reached a certain level. When the engine is cold it dumps extra fuel in to help the car warm up faster. Once the engine is warm it monitors the o2 sensors to keep the car at stoichiometric. Check for Trouble codes using your instrument cluster and if nothing shows up then just wait for the car to warm up before you rev it. Especially if its been sitting for a while and all the oil has leaked down in to the pan, metal on metal is a bad thing, let the oil get inbetween them first.

How long would you need to let it warm up so that the oil has had time to warm up enough? I live less then a mile from the freeway, and then I hop on the freeway to get to work. Is it getting enough time to lube everything in that short amount of time, or should I be giving it about five minutes?

mlambrecht82 · 06-12-2003, 03:46 PM

That depends on a few things. One how long your car has been sitting before you start it up. If it is just over night, then there should still be plenty of oil in the bearings still, if its been a week or more, then all the oil has probably drained back down into the oil pan. The air temperature also plays a big part, when it is cold the oil gets thick, and will take longer to get to all the vital parts in your engine. But thanks to multigrade oil (like 5w-20) the viscocity of the oil is much more stable in low temperatures. In this case at 32 degrees the oil will act as a 5 weight, and at operating temperature the oil will act as a 20 weight. A 20 weight at 32 degrees would take to long to lube up the engine. When the 4.6 first came out they had a lot of problems with them because the customers were putting to thick of oil in there cars. These newer engines have very tight bearing clearances and the tick oils weren't getting pumped through the engine fast enough when it was cold. Customers would bring their cars in very upset complaining that it would run like crap when it was cold, so the technicians would just put a thinner multigrade oil in and the problem was fixed.
If you are in a warm climate, ie above 60 degrees then after driving that car a mile to the freeway the oil will be well distributed, if you are in a colder climate, like 30 degrees then I would let your car sit and warm up for atleast a minute before heading out to work.
You shouldn't have any problems, the thing that you should worry about is starting a cold engine that has sit for a few days and then revving it up as soon as it fires up to make it sound really cool to impress all your sleeping neighbors. The oil deffinately wouldn't of had time to lube everything up and you would be grinding away at all your bearings.
Just make sure that you use the recommended oil for your car, and make sure it is a multigrade.

ajcolv · 06-12-2003, 03:54 PM

Hey thanks. That was a ton of information, and all of it was useful. That's why I like these forums. You learn something new everyday.

mlambrecht82 · 06-12-2003, 04:22 PM

No problem. On top of me learning all these things here at this forum, it also helps me refresh my memory. Helps keep me sharp.

06-06-2003, 12:37 PM	#1
Wikkd GT Registered Member Join Date: Jun 2003 Location: Cincinnati, OH Posts: 12	hesitation when revving engine! I just noticed the other day and also today, that when I start up my 00 GT and the engine is cold, and I put it in neutral and give it some gas to rev it up, it's almost like it bogs down, like it wants to stall out. As if it's not getting enough fuel. Is this normal on the Mustang or is there something that needs to be changed? It only has 26,000 miles on it.

06-06-2003, 06:14 PM	#2
GTJules99 Registered Member Join Date: Jan 2002 Location: Daytona Beach, Florida Posts: 24	My '99 does the same thing. I'm not sure if everyone is like that but it has done this since I bought it. __________________ 1999 Mustang GT - Anniversary, Limited Edition - Silver His name is "Squat."

06-08-2003, 10:28 PM	#3
Badass_yellowGT Registered Member Join Date: Jun 2002 Location: Western,MA Posts: 254	mines does not do that never has anyways you should not rev a cold engine you can do damage let it idle to warm up. it could be caused by the o2 sensors being running in a cold start loop making the engine run to rich the sensors only work after complete engine warm up __________________ Rice Haters Club Member #55 For My car Specs Click the Home page link http://www.badassyellowgt.50g.com/

06-09-2003, 04:30 AM	#4
mlambrecht82 Registered Member Join Date: Oct 2002 Location: Fresno, CA Posts: 101	The sensors do work when the engine is cold, you have HO2S (heated oxygen sensors) so they heat up to over 600 degrees almost instantly, but the engine is in open loop, in other words it disregards the signal from the o2 sensors, until the engine coolant temp. has reached a certain level. When the engine is cold it dumps extra fuel in to help the car warm up faster. Once the engine is warm it monitors the o2 sensors to keep the car at stoichiometric. Check for Trouble codes using your instrument cluster and if nothing shows up then just wait for the car to warm up before you rev it. Especially if its been sitting for a while and all the oil has leaked down in to the pan, metal on metal is a bad thing, let the oil get inbetween them first. __________________ _________________________________ 04 Cobra densecharger CAI BBK off road X pipe Custom Electronic Exhaust cut outs Tuning via Diablo Predator Ported and polished Throttle body and plenum Line locker (for the smoke shows) Stock boost 412 rwhp 379 rwtq

06-12-2003, 03:46 PM	#8
mlambrecht82 Registered Member Join Date: Oct 2002 Location: Fresno, CA Posts: 101	That depends on a few things. One how long your car has been sitting before you start it up. If it is just over night, then there should still be plenty of oil in the bearings still, if its been a week or more, then all the oil has probably drained back down into the oil pan. The air temperature also plays a big part, when it is cold the oil gets thick, and will take longer to get to all the vital parts in your engine. But thanks to multigrade oil (like 5w-20) the viscocity of the oil is much more stable in low temperatures. In this case at 32 degrees the oil will act as a 5 weight, and at operating temperature the oil will act as a 20 weight. A 20 weight at 32 degrees would take to long to lube up the engine. When the 4.6 first came out they had a lot of problems with them because the customers were putting to thick of oil in there cars. These newer engines have very tight bearing clearances and the tick oils weren't getting pumped through the engine fast enough when it was cold. Customers would bring their cars in very upset complaining that it would run like crap when it was cold, so the technicians would just put a thinner multigrade oil in and the problem was fixed. If you are in a warm climate, ie above 60 degrees then after driving that car a mile to the freeway the oil will be well distributed, if you are in a colder climate, like 30 degrees then I would let your car sit and warm up for atleast a minute before heading out to work. You shouldn't have any problems, the thing that you should worry about is starting a cold engine that has sit for a few days and then revving it up as soon as it fires up to make it sound really cool to impress all your sleeping neighbors. The oil deffinately wouldn't of had time to lube everything up and you would be grinding away at all your bearings. Just make sure that you use the recommended oil for your car, and make sure it is a multigrade. __________________ _________________________________ 04 Cobra densecharger CAI BBK off road X pipe Custom Electronic Exhaust cut outs Tuning via Diablo Predator Ported and polished Throttle body and plenum Line locker (for the smoke shows) Stock boost 412 rwhp 379 rwtq

06-09-2003, 11:40 AM	#5
XTheOwl Registered Member Join Date: Mar 2003 Posts: 51	I get the same thing. ('00 GT) I'm not revin it cold, but when I go to back out of the driveway when its cool out, its very hesitent and threatens to stall. xto

06-12-2003, 03:54 PM	#9
ajcolv Registered Member Join Date: Oct 2002 Location: Utah Posts: 58	Hey thanks. That was a ton of information, and all of it was useful. That's why I like these forums. You learn something new everyday.

06-12-2003, 04:22 PM	#10
mlambrecht82 Registered Member Join Date: Oct 2002 Location: Fresno, CA Posts: 101	No problem. On top of me learning all these things here at this forum, it also helps me refresh my memory. Helps keep me sharp. __________________ _________________________________ 04 Cobra densecharger CAI BBK off road X pipe Custom Electronic Exhaust cut outs Tuning via Diablo Predator Ported and polished Throttle body and plenum Line locker (for the smoke shows) Stock boost 412 rwhp 379 rwtq

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